शनिवार, 29 जुलाई 2017


(Chapter – end)
1. Why is the atmosphere essential for life?
Ans. We need atmosphere for following reasons:
(i) It works like a blanket and traps the radiations reflected back from earth surface that keeps the average temperature of earth of quite steady and suitable for sustenance of life.
(ii) It provides carbon dioxide for photosynthesis and oxygen for respiration and combustion.
(iii) Prevents sudden change in temperature.
(iv) Enables us to hear sounds.

2. Why is water essential for life?
Ans. Water essential for life because:
i. All organisms are made up of cells. All cellular processes take place in a water medium. All the reactions that take place within our body and within the cells occur between substances that are dissolved in water.
ii. Substances are also transported from one part of the body to the other in a dissolved form.
iii. Essential for digestion.
iv. Helpful in excretion and egestion.
v. Regulates our body temperature by sweating and evaporation.

3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Ans. Plants need simple nutrients like certain elements for their proper growth and they get most of these elements from soil. With the help of these elements plants prepare their own food in the presence of sunlight. Since all other organisms are dependent upon plants for their nutrition hence we can say that organisms that live in water are not totally independent of soil as a resource. Another reason is that organic matter from soil dissolves into water and provides nutrients to the aquatic organisms.

4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Ans. The weather predictions are made based on information obtained about general patterns of changes in temperature, humidity, winds and clouds.

5. We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
Ans. Isolating many human activities lead to increasing levels of pollution of the air, water-bodies and soil would help in reducing water and soil pollution but it can hardly make any difference to air pollution severity the reason is gases will spread from isolated places and reach everywhere. Instead of isolating we must stress on sustainable management of our resources and cut down or replace their use like using cleaner fuels like CNG in place of fossil fuels.

6. Write a note on how forests influence the quality of our air, soil and water resources.
Ans. Quality of air: Forests have trees and plants that absorb carbon dioxide and liberate oxygen thus maintaining their levels in the biosphere.
Quality of soil: Roots of trees hold the soil particles and prevent soil erosion from taking place. Dead trees and plants or their parts add humus and organic matter to soil thus making it fertile.
Quality of water: Forest allows easy going of the water cycle in nature with cloud formation and condensation in the form of rain.

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